This application claims the benefit of the Korean Application No. P2001-88450 filed in Korea on Dec. 29, 2001, which is hereby incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to a method for making a quantitative analysis of nickel, and more particularly, to a method for making a quantitative analysis of nickel to determine an amount of nickel required for converting amorphous silicon into polycrystalline silicon by MIC (Metal Induced Crystallization).
2. Description of the Related Art
Due to features of the Liquid Crystal Display (LCD), such as a low driving voltage, a low power consumption, full-color realization, light weight, compactness, and the like, application of the LCD varies widely. For example, devices, such as watches, calculators, monitors for PCs, and notebook computers, TVs, instrument panel for an airplane, PDA (Personal Digital Assistants) and mobile stations use an LCD. Typically, an LCD includes a liquid crystal display panel part for displaying a picture, and a circuit part for driving the liquid crystal display panel. The liquid crystal display panel part has a first substrate having thin film transistor (TFT) array formed thereon, a second substrate having color filter array formed thereon, and a liquid crystal layer formed between the two substrates.
The first substrate of the LCD, having the TFT array formed thereon, has a plurality of gatelines arranged in one direction at fixed intervals and a plurality of datalines arranged in a direction perpendicular to the gatelines at fixed intervals. Pixel regions are defined between the gatelines and the datalines. A pixel electrode is formed in each pixel region. A plurality of thin film transistors are formed in the pixel regions adjacent to where the gatelines and the datalines cross, respectively. The gate, source and drain of each thin film transistor are respectively connected to a gateline, dataline and a pixel electrode. Each thin film transistor is turned on/off in response to a driving signal from the gateline such that a picture signal is transmitted from the dataline to the pixel electrode.
The second substrate of the LCD, having the color filter array formed thereon, has a black matrix layer for shielding light from parts of the pixel regions. A RGB color filter layer is formed opposite to the pixel regions for displaying colors. A common electrode is formed on the entire surface of the second substrate, including the color filter layer. In an alternative, the common electrode may be formed on the first substrate in an In Plane Switching (IPS) mode LCD.
The foregoing first and second substrates are bonded together such that a gap is maintained between the two substrates. In the alternative, spacers can be positioned between the substrates to assist in maintaining a uniform gap across the LCD. A liquid crystal layer is positioned in the gap between the two substrates.
In order for an LCD to have high definition and high resolution, especially for moving images, a high speed or highly responsive thin film transistor is required. A high speed thin film transistor requires a high degree of electrophoresis in the active layer of the thin film transistor. Thus, a polycrystalline silicon layer, rather than an amorphous layer, is used to increased the degree of electrophoresis in the active layer. Further, the use of the polycrystalline silicon as an active layer enables cost reduction of a driving Integrated Circuit (IC) by forming the driving IC on the first substrate having the TFT array formed thereon, which facilitates easy fitting since the driving IC is not on a separate substrate. Furthermore, using polycrystalline silicon reduces power consumption since polycrystalline silicon has less resistance than amorphous silicon.
The polycrystalline silicon cannot be deposited directly on the glass substrate of the LCD because of the high temperature for such a polycrystalline deposition. However, amorphous silicon can be deposited on the glass substrate. Then, the amorphous silicon is crystallized into polycrystalline silicon.
The amorphous silicon may be crystallized into polycrystalline silicon by either a solid state crystallizing method or a Continuous Grain Silicon (CGS) method. In the solid state crystallization method, amorphous silicon is deposited on the substrate. The amorphous silicon is then crystallized by using a heat treatment of about 20 hours at 600xc2x0 C. under a vacuum. In the CGS method, amorphous silicon is deposited on the glass substrate, the part in which a channel region of the thin film transistor is to be formed therein is masked off by a silicon oxide film, or the like. Then a Ni layer is deposited on the amorphous silicon such that Ni is not deposited on the channel part and the thickness of Ni on the source/drain regions of the thin film transistor is greater than a few tens of xc3x85. Subsequently, the amorphous silicon is crystallized into polycrystalline silicon. The source and drain regions crystallize due to the Ni on their surfaces and the channel region crystallizes towards its center from the crystallized source and drain regions. The semiconductive properties of the source and drain regions have been diminished because of the large presence of Ni while the channel region is only slightly effected by trace amounts of Ni that may have migrated from the source and drain regions.
Typically, nickel is used when amorphous silicon is crystallized using a metal. Nickel improves speed and completeness of the crystallization of amorphous silicon into polycrystalline silicon. However, too much nickel undermines the semiconductive properties of the subsequently formed polycrystalline silicon. Accordingly, crystallizing amorphous silicon using a nickel needs a method for accurately measuring and/or determining quantity of nickel deposited on amorphous silicon.
A related art method for making quantitative analysis of nickel will be explained, with reference to the attached drawing. FIG. 1 explains a related art method for making a quantitative analysis of nickel. Measuring a thickness of deposited nickel is effective in making a quantitative analysis of nickel. Physical properties of a surface and a thickness of a thin film can be detected by using an ellipsometer. As shown in FIG. 1, an ellipsometer includes a light source 102, a polarizing prism 103 for linearly polarizing light from the light source, a quarter wave compensator 104 for elliptically polarizing the linearly polarized light, an analyzer 105 for analyzing a light that is reflected from and refracted at a specimen 101, and a light detector 106 for detecting the light through the analyzer 105.
A related art method for measuring a thickness of a thin film by using the ellipsometer will be explained in reference to FIG. 1. The polarizing prism 103 and the quarter wave compensator 104 are rotated such that light is having elliptically polarized by the polarizing prism 103 and the quarter wave compensator 104. The elliptically polarized light is incident to a surface of a specimen 101, reflected, and refracted at the specimen 101, is linearly polarized.
Eventually, a thickness of the specimen can be measured by an equation which describes optical characteristics of the specimen 101 and is derived from optical parameters by using rotation angles of the polarizing prism 103, the quarter wave compensator 104, and the analyzer 105. The thickness can be measured to a few thousands of xc3x85. Thus, a thickness of nickel sputtered on amorphous silicon can be measured by using the ellipsometer.
However, the foregoing related art method for making a quantitative analysis of nickel by a thickness measurement using an ellipsometer has the following problems. First, measurement of the thickness is complicated since the thickness is measured by using a polarized light incident to a specimen. Second, the analysis costs are high because of the equipment used to measure thickness with polarized light incident to the specimen. Third, a thickness below 1 xc3x85 can not be measured with an ellipsometer.
Accordingly, the present invention is directed to a method for making quantitative analysis of nickel that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a method for making a quantitative analysis of nickel for crystallizing amorphous silicon in which a solution of a portion of nickel deposited on amorphous silicon is etched by an etchant and subjected to an Energy Dispersive X-ray Fluorescence (ED-XRF) analysis to determine a thickness of the nickel resulting from the deposition process of the nickel.
Another object of the present invention is to provide a method for making a quantitative analysis of nickel for crystallizing amorphous silicon in which an amount of nickel is deposited on an AP1 film and is subjected to an ED-XRF analysis to determine a thickness the of nickel resulting from the deposition process of the nickel.
Another object of the present invention is to crystallize amorphous silicon with nickel deposited on the amorphous silicon in which process parameters of the deposition process are determined from a quantitative analysis of nickel using an ED-XRF analysis.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a method for making a quantitative analysis of nickel includes the steps of providing an amorphous silicon layer, forming an insulating film on the amorphous silicon layer, depositing nickel on the insulating film, etching a defined portion of the nickel with an etchant to create a specimen, drying the specimen on an AP1 film and subjecting the dried specimen to energy dispersive X-ray fluorescence analysis.
In another aspect of the present invention, there is provided a method for making quantitative analysis of nickel that includes the steps of providing a substrate, placing an AP1 film having a predetermined area on the substrate, depositing nickel on the AP1 film, peeling the AP1 off of the substrate and subjecting the peeled AP1 film to energy dispersive X-ray fluorescence analysis.
In another aspect of the present invention, there is provided a method for crystallizing amorphous silicon that includes depositing nickel under different depositing conditions, etching a predetermined area of nickel in each deposition with etchant to prepare specimens for each of the depositing conditions, drying the specimens on AP1 film, subjecting the specimens to energy dispersive X-ray fluorescence analysis, determining an optimal nickel depositing condition according to results of the energy dispersive X-ray fluorescence analyses on the specimens, depositing nickel on amorphous silicon with the optimal depositing condition and crystallizing the amorphous silicon into polycrystalline silicon.
In another aspect of the present invention, there is provided a method for crystallizing amorphous silicon that includes providing substrates, placing an AP1 film having a predetermined area on each of the substrates, depositing nickel on the AP1 film on each substrate such that there are depositions of nickel under different depositing conditions, peeling the AP1 film off of the substrates, subjecting the nickel deposited AP1 film to energy dispersive X-ray fluorescence analysis, determining an optimal nickel depositing condition according to results of the energy dispersive X-ray fluorescence analyses on the specimens, depositing nickel on amorphous silicon with the optimal depositing condition and crystallizing the amorphous silicon into polycrystalline silicon.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory, and are intended to provide further explanation of the invention as claimed.